A vinyl chloride resin is very important as an insulation material because of its excellent properties such as electrical insulating properties, arc resistance, tracking resistance, and dielectric strength compared with rubbers or polyolefins. However, a vinyl chloride resin undergoes reduction in various characteristics due to thermal and oxidative deterioration and becomes unable to withstand practical use.
Furthermore, in wire coating application, a vinyl chloride resin has a problem that it undergoes accelerated oxidative deterioration on contact with copper wire by the catalytic action of copper ions.
It is known to use a heavy metal deactivator, such as a benzotriazole compound, to avoid the adverse influence by copper ions. For example, Patent Document 1 proposes use of a benzotriazole compound having a nitro group, a halogen group or an alkoxy group to stabilize a vinyl chloride resin against thermal hue change, and Patent Document 2 proposes a non-rigid polyvinyl chloride resin composition containing a dialkyl phthalate, chlorinated paraffin, clay, and a benzotriazole compound. However, when these benzotriazole compounds, when added alone, produce only small effects or should be added in relatively large quantities, which has given rise to a problem, such as reduction in coloring resistance or stickiness of the coating compound to copper wire.
Hence, Patent Document 3 proposes addition of a benzotriazole compound combined with a β-diketone compound to a vinyl chloride resin composition for wire coating. The problem of this technique is that satisfactory results are not obtained in some surrounding environments.
Patent Document 4 proposes adding to a synthetic resin a salicylamide compound as a heavy metal deactivator. However, the salicylamide compound produces only a small effect when used alone and should be added in a relatively large amount, which results in damage to coloring resistance and reduction of insulating properties.
Additionally, Patent Document 5 discloses a polyvinyl chloride resin composition for wire coating for wire harnesses containing a benzotriazole compound and a chelating compound such as an amide compound. Nevertheless, there is no mention of synergistic effect by combining specific compounds.
Patent Document 1: JP-B-47-41735
Patent Document 2: JP-A-56-147839
Patent Document 3: JP-A-10-308122
Patent Document 4: JP-A-47-39141
Patent Document 5: JP-A-8-283501